08/12/2025
📉 Case Study: Why Did SPL Drop at the Same 1 kVA Power?
Here’s an interesting case from our amplifier and subwoofer SPL testing. A client reported a sudden 3 dB drop in SPL, even though the power input remained at 1 kVA. Measurements were taken in hybrid SPL+Power mode, showing dB levels, current, voltage, and power. When switching to a different 1000 VA amplifier, the SPL increased by the same 3 dB. 🔊
🔍 Diagnostics & Testing
The client insisted there was no clipping — the clip indicator only lit up at peaks above 1000 VA. I asked for a video of the measurement in PWR mode to analyze not just voltage and current, but also waveform shape and THD %. 🎥
Screenshots revealed:
At low volume, distortion was acceptable (THD < 2%).
As amplitude increased, the sine wave began to square off. Around 800 VA, THD reached ~10%. ⚠
🧠 So What’s Happening to the Decibels?
SPL is measured at the fundamental frequency of the test sine wave. When the signal is clean, most of the energy is concentrated at that frequency — resulting in high SPL.
As distortion increases, energy spreads into harmonics. Total power remains high, but the energy at the fundamental drops — causing SPL to fall, even though the meter still reads ~1 kVA. 🎯
✅ What We Found & Fixed
Turns out the amplifier had elevated distortion after a recent repair. Replacing it with a properly functioning unit restored SPL levels. The faulty amp was sent back to service. 🧰
📌 Key Takeaways
Don’t rely solely on voltage/current readings or the clip light — check waveform shape and THD% in PWR mode.
Use RTA to inspect the output spectrum: the fundamental frequency should dominate over harmonics.
Even if the clip indicator stays off, soft clipping, saturation, or power supply limitations may still be affecting performance.
